The power and the power quality of a circuit arrangement may be determined by measuring the input current and the input voltage. The sensor or the measurement circuit for measuring the input current may need to be isolated, for example for safety reasons, for example by using a coil transformer. However, using a coil transformer may be undesirable as it consumes space and increase the system cost.
As an alternative, the output current and the output voltage may be measured. However, errors are introduced when calculating the power and the power quality of the circuit arrangement based on these measurements. The errors may be particularly large when light loads are connected to the output of the circuit arrangement. For example, the error in calculating the active power may be between 5% to 15%.